In display applications, contrast ratio is the ratio of luminance between the brightest white that can be produced and the darkest black that can be produced. It is a major determinant of perceived image quality. If a displayed image has high contrast ratio, a viewer will judge it to be sharper than a displayed image with lower contrast ratio, even if the lower contrast image has substantially more measurable resolution.
In current digital display applications, the contrast ratio of the displayed images or videos is limited by reflection of ambient light from the display screens in addition to the performance of the projection systems. In particular, the display screens reflect both ambient light and modulated light from spatial light modulators of the display systems onto viewers' eyes without discrimination. Operating display systems in the absence of ambient light will certainly increase the contrast ratio of the displayed images, which, however is not often possible.
A micromirror array device is a type of microelectromechanical device and has found its applications in digital display systems due to many advantages over traditional spatial light modulators, such as LCOS, and LCD. The display systems having micromirror-based spatial light modulators, however, face the same contrast ratio degradation problem as the other type of display systems do.
Therefore, what is needed is a method and apparatus for reducing the impact of the ambient light so as to improve the contrast ratio of the displayed images in display systems having micromirror-based spatial light modulators.